I see SMNs in Abyssea all the time getting insane ammounts of MP back while having an avatar out without any super special gear... Am I missing something? Is there a quest to reduce it? Can someone tell me the right gear I should be using

AF3+2 is the main thing. Specifically, feet, body, and head. With those three pieces, plus a decent staff (perp -3 or more) and Evoker's Ring you should be getting MP back with any avatar out. If you have magian perpetuation staff, you'll probably get 2-3 MP/tick back. The only thing I use which can be annoying to get is the refresh Moonshade Earring which brings me up to 4 MP/tick with avatar out (7 if I cast Refresh). There are also some pants which give refresh, but they're even harder to obtain.

To go beyond that, the only real way to do it is with atma that give refresh. For example in Abyssea if a SMN has trouble keeping MP up they will often use Minikin atma for 10 MP/tick refresh.